Mill control systems



Feb. 1, 1966 R. B. slMs MILL CONTROL SYSTEMS 2 Sheets-Sheet l Filed April 9, 1962 ATTQRNEY Feb. 1, 1966 R. B. slMs MILL CONTROL SYSTEMS '2 Sheets-Sheet 2 Filed April 9, 1962 INVENTQR 5 577775 B2i/M ATTQQNEYS United States Patent() 3,232,084 NELL CONTROL SYSTEMS Raymond Bernard Sims, Shellield, England, assigner to Davy and United Engineering Company Limited, Shel?- field, England Filed Apr. 9, 1962, Ser. No. 186,063 Claims priority, application Great Britain, Apr. 13, 1961, 13,318/ 61 8 Claims. (Cl. 72-16) This invention relates to control systems and is particuarly concerned with automatic gauge control systems for tandem hot strip mills, although the principle may be applied to cold mills.

While automatic gauge control has been applied effectively to reversing mills, using as a gauge detector the Gaugemeter described in my paper in Engineering, January 9, 1953, difficulties have been experienced in applying automatic gauge control to tandemmills. In a tandem mill, if the gauge of the stripdeparts substantially from the nominal value any Iattempt to correct by control of the roll separation on one of the stands'at the end of the train is liable to cause distortion in the shape of the strip; Onthe other hand, correction by control of the'roll separation on astand early in the ltrain is not always feasible, because changes in roll separation haveV a relatively small effect n the iinal thickness of the strip' tected gauge error; in this way, correctionof gauge error` is spread over two or more standsand correction is possible without introducing shape distortion.

The gauge error detector may control the roll separationof the stand on which it is located and the rollseparation on ak preceding Vstand Orstands may be changedy correspondingly. Alternatively, on theoccurrence of a gauge error exceeding a predetermined value, the roll` separation of the stand having the detector of.one or more preceding stands may be changed for predetermined time durations. 1 t

The invention will be more readily understood. by way of example from the following description of tandem mill control systems in accordance therewith, reference-being made to the accompanying drawings, in which FIG- URES 1 and 2 schematically illustrate alternative control systems.

The FIGURE 1 system is shown with a six-stand finishing mill, the stands being^ indicated bythe references F1- F6, and the strip entering the mill at stand F1 and leay, ing from stand F6. Stand F3 hasan automatic gauge control system of the type described in a paper by P. Rf A.-v

riggs and myself in Sheet Metal Industries, March` 1954. Thus, stand F3 has a detector 12 for giving an electrical signal proportional to the rolling load F of the stand.

The roll setting, i.e. the roll vseparation underzero load,.-

is controlled by a screwdown motor 13 driving the screws of the stand through a gearbox 14. A potentiometer 15 is arranged to give an electrical signal representing the amount of screwdown and hencey the roll setting. The datum gauge value at which thestrip, thickness at stand F3 is required to be maintained 'is set by hand or'auto-V matically as hereinafter described on a device 16 and the signals from devices 12, 15, 16 are mixed to give a resultant signal on line 17 representing thedepartu're of the ice gauge from the vdesired value, i.e. the signalon line` 1-'7 represents the gauge error. The gauge error signal on line.17 is applied to an amplifier 18, the output of which is applied to a motor 20 driving, through a gear box 21, al potentiometer 22 and a gauge error indicator 19. Potentiometer 22 is supplied withy a A.C. voltage and the- A.C..output appears on line 23.` At the same time, a second output on line. 24, proportional to that on line 23 is applied to the input of amplifier 1S in opposition to the error signal on line 17. The circuit 18, 20, 21, 22 and 24 operates as a power amplitier, the' potentiometer being driven by motor 20 to maintain the input to amplier 18 substantially 1ero, so thatthe A.C. output on line 23 is accurately proportional to the error signal on line 17 Thesignal on line 23 is applied through contacts 25/1- of a relay 25 tof a remote position control circuit 27 forcontrolling the screwdown motor 13 and hence-the roll setting at stand F3. The signal on line`23 is also appliedthrough resistor R1 to a gate G1. A reference voltage-derived from a potentiometer 26 is similarly applied through. resistors R2, R3 in series to the gate G1 which may consist of a diode rectilier followed by anamplifier, the referenoe voltage from R3 and the signal voltage from R1' being applied to anode and cathode respectively'. A sec ond pair of normally closed contacts 25/2 of relay 25 shorts out resistor. R2, while the output of gate G1 is applied through normally closed contact-s 36/1 of relay 36vv to the relay 25. When the voltage applied to gate G1 from Vline 23 exceeds the voltage G applied'to the gatefrom the potentiometer 26, and not before, gate G1 passes a voltage energizing relay 25 which closes contacts 25/ 1, causing the application of the signal on line 23 to the controlcircuit 27. The-energization of relay 25 also opens contacts 25/2 and puts'resistor R2.in circuit between p0- tentiometer 26 and resistor R3, with the result that relay 25 becomes gie-energized` only when the voltage on line 23 falls below gate value mG, ,where m lies between 0 and 1. For example, if resistors R1, R2 and R3 are equal, relay 25 is energized when the voltage on line 23 exceeds that from potentiometer 26 and is not cie-energized until the voltage on Vline 23 falls to half the voltage from potentiometer 26. Thus, while the gauge error is less than G, the screwdown motor is not controlled and the gauge errorremain-s uncorrected. When the gauge error exceeds G, the screwdown motor isoperated through the control circuit 27 to change the roll separation in a direction reducing the gauge error. When, as a result, the

gaugeerror falls to G/ 2, or to some other preset value,y

less than G, further control of the screwdown motor 13 is prevented..

The roll setting on the preceding stands F1, F2 are made to'follow the changes in the screwdown or roll setting at stand F3 -resulting from the automatic gauge control described above, the intention being that the changes at stands F1, F2 will approximately correct the remain-, ing gauge error G/ 2, so that the correction of the gauge error G is Vspread over the three stands F1-F3. For this purpose, the signal from device 15, representing the roll setting of stand F3 is applied to a follower 28 the shaft 30 of which then has an angular position representing the roll setting. Shaft 30 is coupled through a clutch 31 to a synchro 32 or other remote position control device which transmits the roll separation signal to remote position control circuits 33, 34 for the screwdown motors of stands F1, F2 respectively, with the result that the rolls at stands F 1, F2 are moved by amounts proportional to the movement of the rolls on stand F3.

In operation, on detection of an error exceeding G, the automatic control system operates to reduce the error as described to G/ 2 at stand 3. At the same time, the rolls on stands F1, F2 move with those of stand F3, but the affect of the changes at stands F1, F2 are not immediately apparent at stand F3 and therefore do not affect the operation of the automatic control system. As soon as the changes at stand F3 reduce the gauge error to G/ 2, the control system is cut ofrr by the gate 25 and no further control is exerted unless the gauge error should again exceed G However, the changes at stands F1, F2 in time reduce still further the gauge error at stand F2 to a value which approaches zero.

It will thus be seen that the correction of the gauge error detected at stand F3 is effected jointly by control at stands F1, F2 and F3. If the correction of the gauge error by control of stand F3 only were attempted, the roll forces applied at that stand might become so excessive as to affect the shape of the strip. To prevent dangerous rolling loads being applied at stand F3, a signal on line 35 is -supplied from rolling load detector 12 through a resistor R4 to a second gate G2, which is similar to gate G1 and the output of which controls the relay 36. A voltage representing the maximum permissible rolling load is derived from a potentiometer 40 and applied through a resistor R5 to the gate G2. When the voltage applied through resistor R4 to gate G2 exceeds that applied through resistor R5 to the same gate, the gate energizes relay 36. This has the effect of opening contacts 36/1 between gate G1 and relay 25, thus preventing energization of gate and hence the pas-sage of the gauge error signal on line 23 to operate the screwdown mechanisms.

The datum gauge value may be set by hand on the device 16. Alternatively, when it is more important to obtain material of consistent gauge than to obtain material of a required or nominal gauge, the gauge error detector itself may first be used to set the datum gauge value automatically for a particular strip and all measurements of gauge error thereafter are made with reference to that datum value. For the latter purpose, a self-balancing servo mechanism is used. The gauge error signal on line 17 is applied through a switch 37 to an amplifier 38, the output of which is applied to a motor 39 which drives the device 16 through suitable gearing.

At the start of a strip, the switch 37 is changed over to connect line 17 to amplifier 38. Any error signal appearing on line 17 then operates the motor 39 to alter the setting of device 16 until the error signal on line 17 automatically is brought to zero. The switch 37 is then changed over to apply the signal on line 17 to control the screwdown motors 13, 33, 34 as described in order to keep the strip thickness to the value set up automatically on the device 16.

The system described above and illustrated in FIG- URE 1 entails position control applied to each mill screw or pair of mill screws of each of stands F1, F2, F3. An alternative control system is illustrated in FIGURE 2, where such position control is not required.

The system of FIGURE 2 is generally similar to that of FIGURE 1 and those elements which find their counterparts in FIGURE 1 are given the same reference numerals. Thus, on line 23 there is generated an amplified gauge error signal representing the departure of the thickness of the strip leaving stand F3 from a datum gauge value, set up on device 16 either by hand or by the selfbalancing servo-mechanism 38, 39. The signal on line 23 is applied to a gating circuit 125 which is controlled by a dial 126. The gating circuit 125 is arranged to transmit a signal to a control circuit 127, only when the gauge error signal on line 23 exceeds a prescribed value, G, set on dial 126. Control circuit 127, which includes a timing circuit, applies pulses to timer-s 131, 132, 133, on reception of a signal from gating circuit 125. On being pulsed, each of the timers 131, 132, 133 applies through the respective lines 128, 129, 130 signals of prescribed periods, to the screwdown motors 136, 137, 13 of stands F1, F2, F3 respectively. The periods of the signals on lines 128, 129, 130 can be independently varied by adjustment of the timers 131, 1,32, 133. As a result, the Occurrence of a gauge error exceeding the gating value G results in the operation of the screwdown motors 13, 136, 137 for the prescribed periods, which are selected so that the resulting changes in screwdown Settings approximately reduces the gauge error to zero.

The timing circuit incorporated in the control circuit prevents thevfurther emission of a signal to timers 131, 132, 133 for a-period of time sufficient to enable the gauge error detector to measure the full effect of the changes of roll setting at stands F1, F2, F3. The delay provided by the timing circuit is thus equal to, or slightly greater than, the transit time of strip from stand F1 to stand F3 If, after this time delay, the error signal on line 23 still exceeds the gate value G, the screwdown motors are again operated as above described.

It will be appreciated that the duration of the signal on line is chosen so that the resulting change in screwdown setting at stand F3 corrects a proportion only of the gate gauge error G. Similarly the signals on lines 128, 129 are chosen to produce changes in the screwdown settings of stands F1, F2 which also correct a proportion only of the gauge error. However, the periods of the signals on the three lines 128, 129, 130 are selected so that their total affect on the thickness of the strip being rolled corrects a gauge error of G approximately to zero.

To prevent dangerous rolling loads being applied to stand F3, as before a signal on line 35 is applied from the rolling load detector, through the adjustable limiting device 36 to the control circuit 127, so that if the rolling load exceeds the safe value set in the device 36 the cont-rol circuit 127 is prevented from transmitting a signal to the screwdown motors 136, 137, 13.

In a complete automatic gauge control system for a tandem mill such as that shown in either of the figures, there may be provided, in addition to the circuit operating on stand F3, a second control circuit operating on stand F5. In the case of the control circuit for stand F5, the gauge error detector is similar to that shown for stand F3, but small gauge errors may be corrected by employing the gauge error signal to control automatically the tension between stands F5 and F6, for example by adjustment of the speed of stand F6. If, however, the gauge error exceeds a predetermined value the gauge error signal is applied in addition, by means of a gate similar to gate 25 or gate 125, to control the screwdown or roll setting on both stand F4 and stand F5, in order to reduce the gauge error in the manner already described in relation to stands F1-F3 with reference to either FIGURE l or FIGURE 2. As in the case of stands F1-F3, therefore, large gauge errors detected at stand F5 are corrected jointly by stands F4, F5, although smaller gauge errors are nally corrected in this case by changes in tension following stand F5.

The tensions between consecutive stands of the mill are kept constant by tension detectors L12-L56 which control the preceding stands F1, F2 in the case of tension detector L1.2 and L23, and which control the following stands F4, F5, F6, in the case of the tension detectors L3.4, L4.5 and L5.6, respectively. In the oase of the tensionY between stands F5, F6 the tension detector L5.6 maintains the tension value determined by the automatic gauge control circuit for compensating existing small errors at stand F5. The provision of the automatic tension control systems between consecutive stands of the mill reduces or prevents the eifect of screwdown changes at any one stand on the performance at preceding or following stands.

I claim:

1. An automatic gage control system for a tandem rolling mill comprising detector means at one stand of said mill for giving a signal representing the gage error of the material leaving said one stand, said detector means including means for measuring the rolling load at said one stand, first adjusting means for adjusting the roll setting at said one stand, second adjusting means for adjusting the roll setting of a stand preceding said one stand, means for controlling said irst adjusting means by said gage error signal, and means contr-olled by said first adjusting means for proportionately controlling said second adjusting means.

Z. In a tandem rolling mill having a plurality of stands and a screwdown adjusting mechanism at each stand; an automatic gage control system comprising detector means at one of said stands other than the rst for giving a signal representing the gage error of the material leaving said one stand, said detector means including means for measuring the rolling load at said one stand, means for controlling said screwdown mechanism of said one stand by said gage error signal, and means controlled by said screwdown mechanism of said one stand for proportionately controlling the screwdown mechanism of at least the stand preceding said one stand.

3. In a tandem rolling mill having a plurality of stands and a screwdown adjusting mechanism at each said stand; an automatic gage control system comprising detector means at one of said stands other than the first for giving a signal representing the gage error of the material leaving said one stand, said detector means including means for measuring the rolling load at said one stand, means for controlling said screwdown mechanism at said one stand by said gage error signal, means controlled by said screwdown mechanism of said one stand for proportionately controlling screwdown mechanism of at least the stand preceding said one stand, and means for preventing further adjustment of the screwdown mechanism at said one stand when the gage error has been reduced to a predetermined value exceeding zero.

4. In a tandem rolling mill having a plurality of stands and a screwdown adjusting mechanism at each said stand; an automatic gage control system comprising detector means at one of said stands other than the irst and second for giving a signal representing the gage error of the material leaving said one stand, said detector means including means for measuring the rolling load at said one stand, means for controlling said screwdown mechanism at said one stand by said gage error signal, means for coupling together said screwdown mechanisms of said one stand and the two stands preceding said two stands whereby said mechanisms are adjusted proportionately, and gating means to which said error signal is applied for preventing adjustment of said mechanisms until said gage error exceeds a rst predetermined value, and for thereafter preventing further adjustment of said mechanisms when the gage error is reduced to a second predetermined value less than said first predetermined value.

5. In a tandem rolling mill having a plurality of stands and a screwdown adjusting mechanism at each said stand; an automatic gage control system comprising detector means at one of said stands other than the rst and second for giving an error signal representing the gage error of the material leaving said one stand; said detector means comprising means for giving a irst signal proportional to the rolling load of said one stand, means for giving a second signal proportional to the roll setting at said one stand, adjustable means for giving a third signal proportional to the desired gage, and means for combining said rst, second and third signals to produce said error signal; means for controlling said screwdown mechanism at said one stand by said gage error signal; means for coupling together said screwdown mechanisms of said one stand and of the two stands preceding said one stand whereby said mechanisms are adjusted proportionately; and gating means to which said err-or signal is applied for preventing adjustment of said mechanisms until said gage error exceeds a rst predetermined value, and for thereafter preventing further adjustment of said mechanisms when the gage error is reduced to a second predetermined value less than said first predetermined value.

6. An automatic control system according to claim 5 comprising means controlled by said first signal for preventing operation of said controlling means when said roll-ing load exceeds a preset value.

7. An automatic control system according to claim 5 including means for automatically setting said adjustable means at the start of a rolling operation.

8. An automatic control system according to claim 7 in which there are means responsive to said gage error signal for operating said setting means until the error signal is zero, and means for thereafter rendering inoperative the last mentioned means.

References Cited by the Examiner UNITED STATES PATENTS 2,100,653 11/1937 Umansky 80-35.1 2,933,626 4/1960 Giboney 80-56.1 2,949,799 8/1960 Walker 80--35.1 2,959,992 11/1960 Mitchell 80--56 3,062,078 11/1962 Hulls 80-56.2

OTHER REFERENCES Control Engineering, pages 116, 117, September 1956 (copy in Scientific Library).

CHARLES W. LANHAM, Primary Examiner.

LEON PEAR, WILLIAM I. STEPHENSON,

Examiners. 

1. AN AUTOMATIC GAGE CONTROL SYSTEM FOR A TANDEM ROLLING MILL COMPRISING DETECTOR MEANS AT ONE STAND OF SAID MILL FOR GIVING A SIGNAL REPRESENTING THE GAGE ERROR OF THE MATERIAL LEAVING SAID ONE STAND, SAID DETECTOR MEANS INCLUDING MEANS FOR MEASURING THE ROLLING LOAD OF SAID ONE STAND, FIRST ADJUSTING MEANS FOR ADJUSTING THE ROLL SETTING AT SAID ONE STAND, SECOND AJUSTING MEANS FOR ADJUSTING THE ROLL SETTING OF A STAND PRECEDING SAID ONE STAND, MEANS FOR CONTROLLING SAID FIRST ADJUSTING MEANS BY SAID GAGE ERROR SIGNAL, AND MEANS CONTROLLED BY SAID FIRST AJUSTING MEANS FOR PROPORTIONATELY CONTROLLING SAID SECOND AJUSTING MEANS. 